challenges of underpinning two landmark buildings

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

v O

f So

uth

Aus

tral

ia L

ib o

n 10

/18/

12. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

Challenges of Underpinning Two Landmark Buildings1

Andrew J. Ciancia, P.E.2; Gregory L. Biesiadecki, P.E.3; and Brian E. Ladd, P.E.4

Abstract: Foundation construction adjacent to landmark structures can present numerous challenges for the geotechnical engineer andcontractor, including difficult geology, unexpected subsurface conditions, limited access, and massive and relatively heavily loadedfoundation elements, in addition to being sensitive to their historic fabric. This paper presents two case histories where underpinning wassuccessfully executed in two different geologic settings and utilized various techniques.

DOI: 10.1061/�ASCE�1084-0680�2006�11:3�142�

CE Database subject headings: Foundation construction; Buildings; Historic sites; New York; New York City; Geology.

Introduction

Many buildings that have gained landmark status in New YorkCity were constructed during a time when land was readily avail-able and are usually in desirable real estate markets. Over theyears, many of these structures have undergone numerous addi-tions and renovations, and as such, sometimes have an assemblyof foundation types, sizes, conditions, and bearing elevations.Quite often, improvements and/or new construction are proposedimmediately adjacent to a landmark building, presenting manylogistical, structural and subsurface challenges.

Innovative underpinning techniques are often necessary tosupport historic structures. In addition to the landmark �sensitive�status of the buildings, additional challenges may include adversegeology, limited access, and a change in assumed structuraland/or subsurface conditions revealed during excavation.

This paper presents the challenges faced during the subsurfaceunderpinning of two New York City landmark buildings. The firstproject is a mixed-use 12-story law school building constructedby New York University �NYU� that is located within the Wash-ington Square campus in Manhattan, N.Y. The second project isthe addition of a new entrance pavilion to the Brooklyn Museum,located on Eastern Parkway in Brooklyn, N.Y. Fig. 1 identifies thelocations of the two projects overlain on a surficial geologic map.

1Presented at Specialty Seminar by the ASCE Metropolitan SectionGeotechnical Group and the Geo-Institute of ASCE, May 11–12, 2005,New York City.

2Principal, Langan Engineering and Environmental Services, P.C., 360West 31st St., 8th Floor, New York, NY �corresponding author�. E-mail:[email protected]

3Associate, Langan Engineering and Environmental Services, P.C.,360 West 31st St., 8th Floor, New York, NY.

4Project Manager, Langan Engineering and Environmental Services,P.C., 360 West 31st St., 8th Floor, New York, NY.

Note. Discussion open until January 1, 2007. Separate discussionsmust be submitted for individual papers. To extend the closing date byone month, a written request must be filed with the ASCE ManagingEditor. The manuscript for this paper was submitted for review and pos-sible publication on June 13, 2005; approved on June 13, 2005. Thispaper is part of the Practice Periodical on Structural Design and Con-struction, Vol. 11, No. 3, August 1, 2006. ©ASCE, ISSN 1084-0680/
2006/3-142–148/$25.00.
142 / PRACTICE PERIODICAL ON STRUCTURAL DESIGN AND CONSTRU

Pract. Period. Struct. Des. Con

NYU Mixed-Use Law School Building

NYU constructed a mixed-use law school building �law school�within their Washington Square campus. Prior to construction, thesite was occupied by several four-story turn-of-the century brickand stone structures. The site is bounded by Thompson Street andWest 3rd Street to the east and south, respectively, a NYU lawschool library tunnel built in the 1980s to the west, and a series ofturn of the century buildings to the north. One of the northernbuildings, the landmark Judson Memorial Baptist Church �JudsonChurch�, was designed by McKim, Mead, and White and con-structed circa the late 1880s. Refer to Fig. 2 for the site locationwith respect to adjacent buildings and streets.

The law school consists of an 11–13-story steel framed struc-ture with a brick façade. The foundation footprint is approxi-mately 1,720 m2 �18,500 ft2� and has a two level deep basement.In order to achieve the basement size needed by NYU, the foun-dation walls had to be constructed on the property lines directlyadjacent to the buildings on the west and north sides of the site.

The main geotechnical challenge faced by the designers andcontractor was constructing the basements below the water tablewithout disturbing the adjacent structures and streets. The chal-lenges included underpinning the immediately adjacent buildings,temporarily supporting the active nearby streets, and dewateringthe site, in order to excavate an 11 m �35 ft� deep cut in poorlygraded sandy soils.

Subsurface Conditions

A subsurface investigation was performed that consisted of drill-ing six test borings near and within the footprint of the law schoolsite, and installing two groundwater observation wells. A test pitwas also excavated in the basement of the Judson Church to ob-tain data on the existing foundation. The borings were performedin stages as the existing buildings onsite were demolished. Inaddition, historic boring information of the site was reviewed.Refer to Fig. 2 for the boring and test pit locations.

The generalized subsurface stratigraphy consisted of about3 m �10 ft� of miscellaneous soil and rubble fill, overlying about14 m �45 ft� of glacial sands described as a medium dense, me-dium to fine silty sand, with thin layers of silt. Bedrock, a MicaSchist, was encountered about 17 m �55 ft� below street grade.The groundwater was measured at about a 6.7 m �22 ft� depth. A
generalized east-west subsurface profile is presented in Fig. 3.
CTION © ASCE / AUGUST 2006

str. 2006.11:142-148.

PRACTICE PERIODICAL ON STRUCTU


Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

v O

f So

uth

Aus

tral

ia L

ib o

n 10

/18/

12. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

Foundation System

A mat foundation system bearing on the silty sands, about 11 m�35 ft� below street grade, was selected for the law school. Theaverage �gross� contact pressure of the mat was determined to beabout 120 kPa �1.25 tsf�, which was essentially equal to the ex-isting overburden pressure of the soil at the mat invert. Settlementof the mat was estimated to be about 6 mm �1/4 in.�, mainly fromrecompression �rebound� of the bearing soils during to the exca-vation. The small settlement was not expected to detrimentallyaffect the adjacent structures.

Adjacent Structures

As shown in Fig. 2, existing structures were directly adjacent tothe north and west sides of the law school. Along the entire north-ern side of the site exists the landmark five-story Judson Churchand a series of three- and four-story historic buildings referred toas the Juan Carlos Center. Based on the test pit that was excavatedin the basement, the foundation system of the Judson Church wasobserved to consist of an approximately 0.5 m �20 in.� wide brickand mortar foundation wall bearing on a 1 m �40 in.� wide con-

cation map
Fig. 1. Project lo
Fig. 2. NYU site location plan
crete wall footing. The concrete footing was observed to bear
RAL DESIGN AND CONSTRUCTION © ASCE / AUGUST 2006 / 143

str. 2006.11:142-148.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

v O

f So

uth

Aus

tral

ia L

ib o

n 10

/18/

12. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

directly on the silty sands, about 4.5 m �15 ft� below street grade.The Juan Carlos buildings typically had rear courtyards with dif-ferent property line setbacks, most with planters or block walls atgrade on the property line with a single level basement abuttingthe site. The basement footings below the courtyard were alsobearing on the silty sands but about 3 m �10 ft� below streetgrade. The west limit of the site has a two level deep reinforcedconcrete tunnel structure and thus bearing only several feet abovethe bottom of the final subgrade.

Underpinning and Sheeting/Shoring Systems

The general excavation for the mat extended about 11 m �35 ft�below street grade and nearly 4.5 m �15 ft� below the groundwa-ter table. In order to provide a dry excavation and not to disturbthe bearing soils, a wellpoint system was installed to temporarilyprelower the water table several feet below the final subgrade. Byproperly designing and installing the well point system to mini-mize drawdown of the water level beyond the site limits, theestimated settlement of the nearby structures and streets was es-timated to be small, less than 12 mm �1/2 in.�; the adjacent build-ings in reality did not experience any measurable settlement fromwater lowering.

In order to support the higher elevated structures to the northof the site, but minimize the dewatering schedule �a very costlyoperation�, the decision was made to underpin the historicstructures prior to the start of excavation, using a series ofminicaissons. Available equipment for installation of theminicaissons required headroom of about 10 ft; thus the minicais-sons were installed typically within 1.2 m �4 ft� wide and 3 m�10 ft� high sheeted pits that were excavated directly below theexisting foundations. A total of 11 minicaissons, socketed in thebedrock, were used at the Judson Church. A 245 mm �9 5/8 in.�diameter, 12 mm �1/2 in.� thick steel pipe was drilled to the topof rock and then a typical five foot socket in the rock was createdand then filled with a No. 11 reinforcement bar and concrete.After each minicaisson was completed, the sheeted pit was filledwith 27.6 MPa �4,000 psi� concrete to within 76 mm �3 in.� ofthe underside of the church foundation and later drypacked withsand and cement; steel plates and wedges were used to preloadand obtain positive transfer of building load onto the minicaisson.Thus the upper 10 ft below the Judson Church was continuouslyunderpinned via concrete that was in turn supported by minicais-sons socketed in rock.

Fig. 3. East–West subsurface profile; Manhattan da

A similar system, totaling 11 minicaissons, was used to under-



pin the Juan Carlos Center, except that there was an added com-plication due to some previous underpinning as a result of theNYU library tunnel construction in the 1980s.

In addition to the underpinning elements, the series of minic-aissons along the north side of the site also served as verticalbending elements in the temporary shoring system. An upper tie-back tier was placed about 1.5 m �5 ft� below the bottom of theexisting Judson Church foundation; the tiebacks were drilledthrough the concrete piers and into the silty sands. A second tie-back tier was placed about 3.4 m �11 ft� below the upper tier;these soil anchors were placed inbetween the minicaissons anddouble channel wales were welded to a pair of minicaissons. Thebending capacity of the minicaissons was enhanced with struc-tural tees welded to the exposed face of the steel pipe. Below theconcrete piers, 3-in.-thick timber lagging was used to support thesoil between the minicaissons similar to a conventional soldierbeam and lagging system. The soil anchors were between about11 and 14 m �35 and 45 ft� long with bond lengths between 9 and12 m �30 and 40 ft� in the silty sand. A typical underpinning pierand shoring section along the north wall is shown in Fig. 4.Stressing of the lower tiebacks against the stiffened minicaissonscaused an inward deflection that in turn caused a minor outward

2.75 ft above mean sea level at Sandy Hook, N.J.

Fig. 4. North wall underpinning/shoring section

tum is


str. 2006.11:142-148.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

v O

f So

uth

Aus

tral

ia L

ib o

n 10

/18/

12. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

rotation of the upper underpinning piers; this movement resultedin several “hairline” diagonal cracks at locations of a doorwayand window in the Judson Church.

The existing law library tunnel was located directly to the westside of the site. Since the invert of the law library tunnel was onlyseveral ft higher that excavation subgrade, a conventional under-pinning method—a series of concrete piers—was used to continu-ously underpin the existing foundation wall to below the finalsubgrade level as shown in Fig. 5. Underpinning at the west sidewas performed after the dewatering system was activated.

The two adjacent streets on the east and south sides of the sitewere temporarily supported using a series of HP 12�74 soldierpiles and 3 in. timber lagging laterally retained by two tiers oftiebacks, as shown in Fig. 6. To minimize vibration levels, soldierpiles were predrilled within about 15 m �50 ft� of the JudsonChurch and the law library tunnel. The balance of the soldier pileswere driven to top of rock. As for the north and west sides of the

Fig. 5. Conventional underpinning

Fig. 7. New en



site that were underpinned, two levels of tieback tiers and doublechannel wales were installed as the excavation progressed. Theupper level of tiebacks was positioned to avoid street utilities.

Brooklyn Museum

The Brooklyn Museum, located on Eastern Parkway adjacent toProspect Park and the Brooklyn Botanic Garden, is one of thelargest art museums in the United States. The original McKim,Mead, and White designed Beaux-Arts building first opened in1897 and over the past 100 years has undergone numerous addi-tions and renovations. Continuing the history of upgrades, the

Fig. 6. Soldier piles with tiebacks

ilion and plaza
try pav

str. 2006.11:142-148.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

v O

f So

uth

Aus

tral

ia L

ib o

n 10

/18/

12. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

1986 master plan included the reconstruction of the entrancealong Eastern Parkway. Renovation of the entrance included anew glass pavilion, lobby, and outdoor public plaza. Fig. 7 is acopy of a photograph of the completed entrance upgrade. Theproject improved visitor access and updated amenities, and cre-ated new basement space that houses mechanical equipment forthe entire museum.

Foundation construction extended from about the middle ofthe existing east wing �left side in Fig. 7� across the main entryportico and the full length of the west wing. The previous en-trance to the museum was from the former ground level of el47.85 m �elevation 157 ft� through five massive brick columnsthat support limestone columns above. Footings supporting thebrick columns were bearing at elevation 46.79 m �153.5 ft�;whereas, the top of finished floor elevation of the new basementspace adjacent to the brick columns was at elevation 44.88 m�147.25 ft�. Therefore, underpinning of the five large brick col-umns was required. The continuous wall footing of the existingwest wing stepped up from elevation 45.26 m �148.5 ft� at themain entry portico to elevation 50.08 m �164.3 ft� at the far westend. The bottoms of new basement footings varied from elevation42.14 m �138.25 ft� near the entrance portico up to elevation47.63 m �156.25 ft� at the west end of the wing; underpinning thefull length of the existing west wing was required. The existingfaçade of the east wing was far enough removed such that under-pinning was not required. Only a portion of the areaway just eastof the main entry portico had to be underpinned.

Subsurface Conditions

The Brooklyn Museum is situated within a terminal moraine, aridge of glacial deposits formed at the southernmost limit of aglacial advance. These deposits, known as glacial till, are charac-terized by very dense silt and sand deposits containing gravel, andnumerous cobbles and boulders.

Prior to underpinning, a subsurface investigation was con-ducted, including drilling eight test borings around the perimeterof the existing museum building, three of which were locatedalong the north facade. Borings were advanced to depths of be-tween about 11 and 16 m �37 to 52 ft� below grade. Standardpenetration testing �SPT� and split spoon sampling was conductedat 1.5 m �5 ft� intervals. Due to site constraints, test pits could notbe performed. The generalized stratigraphy consisted of a layer ofsurficial fill underlain by glacial till. A typical subsurface crosssection is shown in Fig. 8.

The overlying fill was brown, silty, fine to medium sand con-taining gravel, brick, and concrete fragments. The thickness of thefill layer ranged from about 1.5 to 3 m �5–10 ft� with SPT N

Fig. 8. Brooklyn Museum subsurface profile; elevations referencedare relative to Borough President of Brooklyn datum, which is 2.56 ftabove mean sea level at Sandy Hook, N.J.

values ranging from 14 to 55 blows per 30 cm �1 ft�.



Below the fill was a brown, medium to fine sand deposit withsome silt, containing varying amounts of gravel, cobbles, andboulders �glacial till�. SPT N values ranged from 34 blows per30 cm to more than 100 blows per 15 cm �6 in.� of split spoonpenetration. The high N values indicated a very dense depositand/or the presence of the cobbles and boulders that impededadvancement of the split spoon sampler. Large boulders, some asmuch as 1.5 m �5 ft� across, were encountered in most of theborings. The borings were terminated within the glacial till de-posit before rock was encountered. Bedrock is believed to bemore than 60 m �200 ft� deep in this area of Brooklyn. Ground-water measurements taken in a piezometer and in completed bore-holes indicated that the water level was well below the proposedsubgrade elevation.

Underpinning

About 104 lineal m �340 ft� of the existing north façade requiredunderpinning. This included a short section of the east wing�10.4 m/34 ft�, the front brick columns �30.5 m/100 ft�, porticowalls and reentrant columns �23.2 m/76 ft�, and the entire westwing �39 m/128 ft�. The challenging aspects of this project werethe massive size of the brick columns at the entrance, the thick-ness, and relatively heavy loads of the façade walls, limited ac-cessibility to the reentrant columns at the rear of the entranceportico, and excavation of underpinning pits in the very denseterminal moraine soils. The following description of the underpin-ning work is presented in the general order in which it wasinitiated.

West Wing WallThe widths of the existing west wing wall were as follows: be-ginning at the main entry portico and extending 7.6 m �25 ft�, thewall was 1.8 m �6 ft� wide; from 7.6 m �25 ft� and continuing tothe west end of the wall, the width was 1.5 m �5 ft�. A concretefooting protruded 45 cm �18 in.� from the face of the wall. Theexisting footing loads were estimated by the structural engineer to

Fig. 9. West wing wall underpinning

be 0.48 MPa �5 tsf�. The height of the underpinning piers would


str. 2006.11:142-148.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

v O

f So

uth

Aus

tral

ia L

ib o

n 10

/18/

12. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

be up to 5.2 m �17 ft� and a portion of these higher underpinningpiers were to be left permanently exposed in a stairwell.

The design plans called for underpinning the wall its fullwidth; however, the contractor initially attempted to install anunderpinning pier that was only 1 m �3 ft� wide. Taking into ac-count the concrete footing protrusion, the pier would only extendabout 45 cm �1 1/2 ft� beneath the 1.83 m �6 ft� wide section ofthe wall. This was considered unacceptable and work wasstopped. The goal was to �1� transfer the entire wall load to soilbelow the new basement, maintaining the original bearing pres-sure to minimize differential settlement; and �2� not induce addi-tional lateral pressure onto the back of the underpinning piers dueto existing wall loads being transferred to soil. Note that at thispoint, shop drawings had not been submitted by the contractor.

To facilitate access and allow underpinning of the full wallwidth, the 45 cm �18 in.� thick concrete footing protrusion wastrimmed flush with the face of the façade. This increased the wallbearing pressure to about 0.57 MPa �6 tsf�, which the glacial tillwas deemed able to support. The portion of the underpinningpiers above the new basement slab on grade was constructed to be1.5 m �5 ft� wide �full wall width� and the portion below the newslab could be reduced to 1.22 m �4 ft� thick. Soil anchors wereinstalled to provide lateral support for underpinning piers greaterthan 3 m �10 ft� in height. Piers less than 3 m �10 ft� tall wouldbe dowelled into the underside of the wall footing with no soilanchors. Fig. 9 is a sketch of the underpinning piers installedbelow the west wing wall.

Brick Columns of Entrance PorticoThe six, 2.44 m �8 ft� by 2.44 m �8 ft� brick columns of the en-trance portico were supported on 3.66 m �12 ft� by 3.66 m �12 ft�brick pedestals that extend laterally 60 cm �2 ft� beyond the faceof the brick column on all sides. The pedestal in turn bears on aconcrete “bulb.” The concrete “bulbs” were founded at elevation45.732 m �150 ft� and appeared to have been rough cast, havingvariable thicknesses and lateral shapes. The load in the brick col-umns was estimated at 4.45 kN �1,000 kips� �about 3.1 MPa

Fig. 10. Brick column underpinning

�3.2 tsf� average bearing�. The initial underpinning scheme called



for full underpinning of the columns and would require trimmingof the concrete bulb to gain access between adjacent columns.

After trimming the concrete bulb and brick pedestal to withinabout 15 cm �6 in.� of the front face of the brick columns, thereduced bearing area resulted in a contact pressure of about0.48 MPa �5 tsf�. The underpinning piers for the brick columnswould be about 1.83 m �6 ft� tall and soil bermed against theirtoe. Due to the relatively short unsupported height of the under-pinning piers and the contact pressure of the column footingsbeing less than allowable for the glacial till, the brick columnswere allowed to be underpinned only beneath their front �north�edge.

Each underpinning pit was to be excavated a maximum widthof 1.22 m �4 ft� and extended beneath each column a minimumdistance of 1.22 m �4 ft� from the front face. Each of the 1.83 m�6 ft� high piers was dowelled into the underside of the concretebulbs. Fig. 10 shows the underpinning design for the six brickentrance columns.

Reentrant ColumnsAt the rear of the entrance portico, on both the east and westsides, were large brick reentrant columns. Each of these columnssupported an estimated 6,450 kN �1,450 kips� and were bearingon large “stepped” brick and concrete footings that are about5.18 m2 �17 ft2� or 26.85 m2 �289 ft2�. Two new columns wereadded to these large footings and imposed additional loads of956 kN �215 kips� and 833 kN �185 kips� onto the stepped foot-ings, resulting in a new total load on each reentrant column foot-ing of about 8,230 kN �1,850 kips�.

To fully underpin these footings, access to the rear of the foot-ings would be required from the lobby inside the existing mu-seum. During installation of underpinning for the portico andwing walls, soil beneath the exposed front edge of the steppedfootings was disturbed.

After addition of the two new columns, the contact pressure ofthe stepped footing would be about 287 kPa �3 tsf�, less than halfthe allowable bearing pressure of the glacial till. The height ofunderpinning would be about 1.22 m �4 ft�. Similar to the brickcolumns at the entrance, it was judged that the reentrant columns

Fig. 11. Reentrant column underpinning

did not require full underpinning.


str. 2006.11:142-148.

Dow

nloa

ded

from

asc

elib

rary

.org

by

Uni

v O

f So

uth

Aus

tral

ia L

ib o

n 10

/18/

12. C

opyr

ight

ASC

E. F

or p

erso

nal u

se o

nly;

all

righ

ts r

eser

ved.

The previously disturbed soil was removed to a depth of1.52 m �5 ft� beneath the front edge of the reentrant column foot-ings and the excavated areas underpinned. The underpinning pierswere constructed diagonally from the portico wall to the adjacentwing wall. To construct the full length of the diagonal, the dis-turbed soil was successively excavated in 1.22 m �4 ft� wide in-crements. Fig. 11 shows the plan view for underpinning of thereentrant columns.

Underpinning Pier ConstructionThe underpinning pits were excavated using a Hitachi EX200-LCexcavator. The glacial till contained numerous cobbles and boul-ders that made excavation difficult. The decision to remove theboulders was judged on a case by case basis. If the obstructioncould not be removed without risk of undermining the wall orleaving a large void in the back face of the underpinning pit, thenthe boulder was left in place. The sides of the pits were supportedwith timber lagging and plywood. Lagging was either not placedagainst the rear of the pit or was removed at the time of concreteplacement, so that concrete could be placed against the exposedsoil. It was desired not to have voids, resulting from boulderremoval, left behind the sheeting. The underpinning pits werefilled with concrete the same day of excavation and were dry-packed the following day.

Lateral support was provided for underpinning along the westwing wall by seven soil anchors. The anchors were constructed byinstalling a 35 mm �1 3/8 in.� diameter, grade 150 thread bar in a63.5 mm �2 1/2 in.� diameter borehole. The holes were drilled at30° from horizontal, spaced at 3.66 m �12 ft� on-center. Using asoil–grout adhesion of about 290 kPa �42 psi�, a 3.66 m �12 ft�bond length was determined for the 48 kip lock-off load. The totallength of each anchor was about 8.23 m �27 ft�.

Summary and Conclusions

NYU Law School

Overall, the system designed and the installation procedures em-ployed by the contractor allowed for the successful constructionof the NYU Law School despite the many challenges of thisproject. Key issues were as follows:



1. Understanding of the site constraints by all parties;2. The willingness on the owner’s part to finance the proper

means to achieve the desired results;3. A contractor experienced in underground construction in an

urban environment;4. Interaction between the engineer and the contractor was an

important element in contributing to timely resolution of un-derpinning challenges; and

5. The successful use of minicaissons allowed the underpinningprogram to be completed prior to the start of the costly�round the clock� dewatering operations.

Brooklyn Museum

The underpinning of the north façade of the Brooklyn Museumsuccessfully held up the landmarked building and provided exca-vation support during construction of the new entrance pavilion.Observations made during the project were as follows:1. The museum’s schedule and public access requirements al-

lowed only for a limited test boring program. Knowledge ofthe area’s geology lead to the expectation of encounteringnumerous boulders during excavation and underpinning op-erations. Including test pits as part of the exploration pro-gram would have helped define the boulder content withinthe terminal moraine.

2. A “preunderpinning” meeting would have established that allparties understood and agreed on the scope of work.

3. Be prepared to modify underpinning schemes as field condi-tions are revealed. Interaction with the design team, con-struction manager, and contractor contributed to a timely de-cision on a prudent underpinning scheme.

4. The relatively heavy wall loads of the existing west wing inconjunction with tall unsupported height of the underpinningpiers required full width underpinning of the museum walls.

5. The very dense terminal moraine soil provided more thanadequate support for the existing large brick entrance andreentrant column footings, allowing for partial underpinningof these elements.

6. Vibrations measured on the 3rd floor were less than 6 mm�0.25 in./ s� and the level line survey monitoring of the northfaçade showed movements to be less than 6 mm �1/4 in.�.The historic museum was found to tolerate the movementsand vibrations associated with the underpinning operations.


str. 2006.11:142-148.

challenges of underpinning two landmark buildings

Documents